2000 blazer will not crank aka turn over
 

Working on 2000 s10 blazer 4x4 4.3 auto with 110000 miles... Ok this started after I replaced the transmission worked fine before. After replacing the tranny it started fine for 4 days, now I turn the key and nothing happens.

You can here the fuel pump kick on all dash lights come on as usual. Security light comes on and goes out like it should. I have 12.1 volts at the starter relay at the larger oranage wire on the relay terminal 87. and no power at the purple wire terminal 30 when turning the key.

All drive positions on dash work correctly reverse overdrive drive 2and 1 ... I'm confused what to try next any ideas.? And before tis is asked yes connection at battery are clean. And ground is clean and tight as well. So far This is what ive tried. I replaced the ignition switch, the neutral safety switch, the relay on the firewall and this thing still will not start.

There's 5 wires for the starter relay on the firewall
30 witch is purple. Witch goes to starter solenoid (I get no power to this wire)
86 witch is orange No power to this wire
87 orange as well but a larger gauge (good power of 21.1 volts)
87a. Blue No power
85. Black

Now i have power on terminal 87 but no power to any other wire on the relay.

Ive checked all fuses and cant find one blown. My understanding is ignition a powers that purple wire that fuse is fine.

when you turn the key in crank position you hear and feel the starter relay in the fuse distribution block on drivers fender click but nothing happens.

Any help would be much appreciated, im lost on what to try next.

Ok narrowed it down to the wire harness that runs down the drivers side of the transmission, when you pull that harness it startes up.

With those color wires, you're testing the heater blower relay :)

Crappy connection at the neutral safety switch on the transmission?

At the starter relay in the underhood fuse panel:
Terminal #30, Red wire must have battery voltage at all times.
Terminal #87, Purple wire goes to starter solenoid.
If you jump #30 to #87, the starter must engage.

Terminals #85 & #86 are the trigger circuits for the relay.
Terminal #86, Black wire goes to ground. Must have less than 5 ohms resistance to ground at all times.
Terminal #85, Purple with white trace wire comes from neutral safety switch. Must have battery voltage in START position.

Wow thanks captain hook i could of used that information a couple days ago. ive been chasing the wrong power source. I do feel like a idiot now for not following that purple wire to find that out sooner.

No problem. No need to struggle with stuff, just ask, that's why we're here. If there's a problem with a Blazer, no doubt we've seen it at least once here on the forum ;)

Check the circuits, (in post #3) at the relay. Then post your results here, we'll point you in the right direction.

Having this same problem
 

I'm having this same exact problem with my 2000 blazer. Can someone please help me with this situation? I would very much appreciate it!

find the starter relay under the hood.

Check for always on 12V on pin 30

Check for 12V on pin 85 during key to start.

Check for 12V passed to pin 87 during key to start.

Check for always on 12V at starter black cable

check for 12V at starter purple wire during key to start.

Some huys would do this in the reverse order which is OK too. Let us know what you find.

George

Figured it out!
 

So I tested everything you all said here. I jumped 30-87 to see if the starter would crank, and it did. My battery was only reading 11.9V, so I had someone turn the key while I was jumping the starter relay to see if it would turn over, and it did - and died 3 seconds later, as I figured it would. Instead of going into the ignition switch wires and testing all that, I decided to go with the best easiest test... And thankfully I found my problem! Or at least some of it.

Answer? Neutral Safety Switch. I put the truck in neutral and it started up beautifully. Smh, wish I would have thought to check that in the beginning! It definitely would have saved a huge headache throughout my day today lol.

Thanks for the help!